1. Field of the Invention
The invention relates to a ground connection for electronic devices, in accordance with the preamble of claim 1, together with a method for making such a ground connection, in particular for gearbox or engine controllers in the automobile industry.
2. Prior Art
Modern mechatronics, that is to say in particular control electronics, which are installed directly where used, for example in a gearbox or engine, are subject to numerous environmentally-determined requirements. Apart from the long-term stability and security against failure of the controller, the raised operating temperatures and the mechanically demanding environment in the engine or gearbox, due to the constant vibrational stresses, are at the forefront. It is therefore imperative that the sensitive electronics are, as far as possible, protected from these influences. In addition to this, the strict requirements for electromagnetic screening play a role which is becoming ever greater because, in particular in the engine compartment, numerous electronic units and computer parts are brought together. Especially the design of the ground connection points for the electronic units represents a major challenge.
There are various known concepts for attaching the ground connection for electronic devices, for example in the engine controller, to the engine block. For example, there is often simply a pre-assembled conductor, such as for example a flexible copper lead fitted with an eye which can then be bolted onto the chassis or the engine block.
A conventional ground connection of this type exhibits several disadvantages. On the one hand, assembly faults can occur during mounting of the device or later during repair work. This may lead to an increase in the electrical contact resistance for the grounding connection, and to malfunctions of the device. On the other hand, this type of grounding connection calls for a relatively large number of individual parts which must be assembled one after the other, and thus to increased assembly costs.
DE 101 36 361 A1 describes a concept for making electrical contact to ground potential for a foil conductor. For this purpose, a ground bolt in the form of a thread on the housing and a special multi-part wing-screw which in a flat area has a holder for foil conductors are provided. At the same time, it also remains possible to affix and make contact with a conventional round conductor, using the screw.
DE 10 2004 041 169 B3 also describes an arrangement for making a grounding connection for an electrical circuit substrate. It proposes the provision of a plug connector between a circuit substrate and the grounding conductor, having a pin and a corresponding recess on the housing side, where the plug connector is embodied as an interference fit. The number and shape of the ground pins can here be designed flexibly.
The disadvantage of ground connections embodied in this way is that the concept can only be applied to the particular special grounding contact-making by means of a recess which must be provided on the housing side. Hence a prerequisite per se of these concepts is that it is necessary to form a special ground connection, either as a threaded bolt or as a recess on the grounding conductor. In addition, this calls for an increased accuracy of fit for the entire component arrangement relative to the special connection on the grounding conductor.
Over and above this, the known ground connections have little flexibility, and so are susceptible to failure over the course of the entire service life if the housing and components are subject to severe vibrations.
In this context, various oscillation dampers have been developed in the most recent past, for suspending a control electronics unit on housings.
Thus, an oscillation damper with a damping element made of elastic material is known from DE 199 51 265 A1, this being surrounded by a cup-shaped metal part. The interior space in the half-shell metal part is preferably closed off by a flexible part which can consist, in particular, of an electrically-conducting woven fabric. In this way, it ensures that the joint, between the two metal bolts which are fixed in opposing positions and which serve to affix the oscillation damper to the housing, is a good conductor. In this way, a grounding connection can be established via the electrically-conducting woven fabric.
A disadvantage of this development of the grounding connection is the fact that, due to the electrically conducting woven fabric, it is not sufficiently robust to provide problem-free contact-making over the entire service life of the engine or the gearbox, in an environment which is aggressive both mechanically and also chemically, and due to the temperatures. In addition, this design of oscillation damper is expensive and calls for the precise-fitting use of the expensive special woven fabric.